1. Field of the Invention
This invention relates to biological methods and products useful for the control of Solenopsis invicta. More specifically, the present invention is directed to a novel Solenopsis invicta virus, nucleic acids encoding the novel virus, biocontrol compositions, and methods of using the virus and/or biocontrol compositions for control of fire ants.
2. Description of the Related Art
Red imported fire ant, Solenopsis invicta (Buren), was first detected in the United States near Mobile, Ala. in the late 1920s (Loding, USDA Insect Pest Surv. Bull., Volume 9, 241, 1929). Since that time, it has spread to encompass more than 128 million hectares, from Virgina, south to Florida and west to California. (Williams et al., Am. Entomol., Volume 47, 146-159, 2001). Efforts to control, prevent, repair damage, and otherwise to mitigate the effects of this pest ant are estimated to exceed 3 billion dollars annually (Pereira, J. Agric. Urban Entomol., Volume 20, 123-130, 2004). Fire ants are known to destroy young citrus trees, growing crops, and germinating seeds. This has an economic impact on agriculture in infested areas. Telephone companies spend substantial amounts of money each year treating their electrical equipment to prevent fire ant invasion because fire ants accumulate at electrical contacts and can short out electrical equipment. Farm equipment can also be damaged by large fire ant mounds. Fire ants also present a danger to wildlife, such as ground nesting birds and animals. Furthermore, fire ants are known to excavate the soil from under roadways causing damage.
Fire ants also pose health care problems to millions of people stung each year—a significant number of which require medical care. Fire ant stings are also blamed for human deaths. Consequently, there is much interest in controlling these troublesome pests.
This interest has resulted in much research and resources being expended through the years to develop reagents and methods for controlling fire ants. While many useful insecticide formulations have resulted from this research, the problems associated with fire ants still exist because the relief gained by insecticide use is only temporary. Once the insecticide pressure is relaxed, fire ant populations invariably repopulate the areas. This reinfestation ability is attributed to the high reproductive capabilities, the efficient foraging behavior, and the ecological adaptability of the ants. While effective for controlling ants in relatively small defined areas, insecticides can create other problems. For example, some insecticides, which are effective at controlling fire ants, can pose a significant threat to the environment, including birds and mammals.
Although considerable research effort has been brought to bear against the red imported fire ant, it remains the primary pest ant species in infested areas; initial eradication trials failed, yielding to the wide distribution of pesticide-based control products and a federally imposed quarantine to prevent further spread. Recently, much of the research effort has focused on elucidating basic life processes in an attempt to develop unique control measures, and fostering the development of self-sustaining methods of control, including biocontrol organisms and microbes (Williams et al., Am. Entomol., Volume 49, 150-163, 2003).
Despite intensive searches over the last 4 or 5 decades for viral infections of S. invicta, only recently were the first viral infections reported and characterized from this ant (Valles et al, Virology, Volume 328, 151-157,2004; Valles and Strong, 2005; Valles et al., Virology, Volume 365, 457-463, 2007; J. Invert. Pathol., Volume 99, 74-81, 2008). Solenopsis invicta virus 1 (SINV-1) is a positive-strand, RNA virus with characteristics consistent with viruses in the Dicistroviridae (Mayo, Arch. Virol., Volume 147, 1655-1656, 2002). It possess a monopartite, single-stranded, 3′-polyadenylated, RNA genome that encodes 2 polyproteins. The 5′-proximal polyprotein contains sequences with identity to RNA-dependent RNA polymerase (RdRp), helicase, and cysteine protease proteins characteristic of single-stranded RNA viruses (Koonin, J. Gen. Virol., Volume 72, 2197-2206, 1991) and the 3′-proximal polyprotein contains sequences consistent with viral coat proteins which was confirmed by purification and N-terminal sequencing (Hashimoto and Valles, J. Invertebr. Pathol., Volume 99, 136-140, 2008). Solenopsis invicta virus 2 (SINV-2) is also a positive-strand RNA virus but with an unusual genome organization (Valles et al., 2007, supra). The SINV-2 genome is monopartite and polycistronic, with 4 open reading frames in the sense orientation (Valles et al., 2007, supra). SINV-1 and-2 have been associated inconsistently with colony death (Valles et al., 2004; 2007; Hashimoto and Valles, 2008, supra).
Use of positive-strand RNA viruses as insect control agents has been proposed (Scotti et al., Adv. Virus Res. Volume 26, 117-143, 1981; Insect viruses: new strategies for pest control, 128-163. In Oakshott, J. Whitten, M. J. (eds) Molecular approaches to fundamental and applied entomology. Springer Verlag, New York, N.Y. et al, 1993) and successfully demonstrated for the olive fruit fly (Manousis and Moore, Appl. Environ. Microbiol., Volume 53, 142-148, 1987) and Helicoverpa armigera (Christian et al., J. Econ. Entomol., Volume 98, 1839-1847, 2005). However, production of pure virus has been limited to in vitro systems (cell culture). A cell line is not available for S. invicta which has hampered development and use of the Solenopsis invicta viruses as control agents against fire ants. Recently, successful in vitro expression of a positive-strand RNA virus was reported (Pal et al., J. Virol., Volume 81, 9339-9345, 2007; Boyapalle et al. Virology, Volume 375, 401-411, 2008). A clone of the Rhopalosiphum padi virus genome was expressed in a baculovirus expression system and found to be infectious and pathogenic to its aphid host (Pal et al., 2007; Boyapalle et al., 2008; both supra).
A dearth of natural enemies of the red imported fire ant have been found in the U.S. including a neogregarine (Pereira et al., J. Invertebr. Pathology, Volume 81, 45-48, 2002) and a fungus (Pereira et al., J. Invertebr. Pathology, Volume 84, 38-44, 2004).
U.S. Pat. No. 6,660,290 discloses a non-sporulating mycelial stage of an insect-specific parasitic fungi for control of pests with fire ants listed as one of many examples of insects controlled by the biopesticide.
U.S. Pat. Nos. 4,925,663; 5,683,689; 6,254,864; and 6,403,085 disclose a biopesticide effective against fire ants that includes the fungus Beauveria bassiana. 
There remains a need for biocontrol and/or microbial control agents that eliminate or at least reduce the spread of fire ant colonies using novel pathogens. The present invention described below is directed to a novel Solenopsis invicta virus useful for the control of fire ants which are different from prior art pathogens and their uses.